The CAS Registry Mumber 104751-91-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,4,7,5 and 1 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 104751-91: (8*1)+(7*0)+(6*4)+(5*7)+(4*5)+(3*1)+(2*9)+(1*1)=109 109 % 10 = 9 So 104751-91-9 is a valid CAS Registry Number.